Altered kinetics of an intravenous calcium load in hypertensive patients.

Essential hypertensive (EH) patients have a higher rate of urinary calcium excretion and, according to some reports, somewhat lower levels of serum ionized calcium. The aim of this study was to investigate the kinetics of an i.v. calcium load in EH patients and in normotensive controls. Fifteen EH patients and twelve sex-and weight-matched controls received a constant ionized rate i.v. calcium infusion (0.1 mmol Ca2+/kg body weight/h) for 2 h. Serum ionized calcium and urinary calcium excretion were determined at regular intervals during the infusion and, in two subgroups of seven hypertensives and seven controls, for up to 4 hours later. EH patients had significantly higher excretion rates (P less than (P less than 0.001) and slightly, but not significantly, lower serum ionized calcium compared to controls. The serum ionized calcium concentration attained at 60 and 120 min of the Ca2+ infusion was significantly lower in EH (P less than 0.01) and it remained appreciably lower for up to 220 min from the beginning of the test. The area under the curve of serum ionized calcium calculated at different time points was significantly reduced in the hypertensives. The mean renal calcium clearance of the patients during the infusion and the elimination phase was somewhat higher, but the difference from controls did not reach statistical significance. These data indicate an abnormal handling of a calcium load by patients with EH and raise the possibility that such abnormality may not be due simply to a renal defect but perhaps to an altered calcium distribution among different compartments in the body.